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DESIGN & CONSTRUCTION GUIDELINES

FOR A

SOIL NAIL WALL SYSTEM

GEOTECHNICAL ENGINEERING MANUAL

GEM-21

Revision #4

AUGUST 2015

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EB 15-025 Page 1 of 13

GEOTECHNICAL ENGINEERING MANUAL:

DESIGN & CONSTRUCTION GUIDELINES FOR A SOIL NAIL WALL SYSTEM

GEM-21

Revision #4

STATE OF NEW YORK

DEPARTMENT OF TRANSPORTATION

GEOTECHNICAL ENGINEERING BUREAU

AUGUST 2015

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EB 15-025 Page 2 of 13

TABLE OF CONTENTS

I. DESIGN ....................................................................................................................................3

A. Consultation .................................................................................................3

1. Temporary or Permanent Soil Nail Walls ....................................................3B. Feasibility Analysis ......................................................................................3

C. General Layout .............................................................................................4

II. CONSTRUCTION ..................................................................................................................6

A. Consultation .................................................................................................6

B. Design Submittals ........................................................................................6

C. Materials ......................................................................................................6

D. Monitoring Nail Installation.........................................................................7

1. Excavation....................................................................................................7

2. Drilling .........................................................................................................8

3. Nail Installation ............................................................................................8

4. Grouting .......................................................................................................8

E. Supervising Nail Stressing & Testing ..........................................................9

F. Temporary Shotcrete Construction Facing & Drainage Examination .......11

G. Documentation ...........................................................................................11

REFERENCES ..............................................................................................................................12

APPENDICES ...............................................................................................................................13

A. Soil Nail Installation Forms (US Customary Units) ............................... A-1

B. Soil Nail Installation Forms (International System of Units) .................. B-1

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I. DESIGN

A. Consultation

The Designer shall consult with the Regional Geotechnical Engineer (RGE) as early as possible

in the design phase to ensure adequate subsurface explorations are progressed to verify thefeasibility of installing the soil nail wall system. Subsurface explorations must also provide

enough information to define the engineering characteristics of the soil for design purposes.

When considering the use of a soil nail wall system, it is recommended that the Designer contact

the RGE for the determination of the appropriate subsurface exploration locations and

subsequent analysis of the soil for its suitability for soil nailing. The Designer and the RGE shall

also discuss the groundwater elevation and its effect on the proposed soil nail wall system and

the anticipated construction sequencing with regard to the work zone traffic control to determine

if additional subsurface explorations are required.

1. Temporary or Permanent Soil Nail Walls:

A structure with a service life of 18 months or less qualifies as temporary. A structure

with a service life longer than 18 months qualifies as permanent. If a structure is initially

intended as temporary (e.g. temporary support of an excavation) but the results of the

discussions between the Designer and RGE indicate that substantial construction delays

are expected which dictate the excavation remain open much longer than 18 months, the

soil nail wall should be characterized as permanent.

B. Feasibility Analysis

Although the details of the soil nail wall system will be designed by the Contractors consultant,

a feasibility analysis is recommended. The Designer and the RGE shall request the Geotechnical

Engineering Bureau (GEB) for a feasibility analysis. This analysis shall include:

1. Investigation of the site to determine if the subsoils are appropriate for soil nailing. Some

limitations to soil nails are:

A. Excavation support: To construct a soil nail wall, the first step is to make a near

vertical excavation approximately 3 ft. to 6 ft. (1 m to 2 m) high. Therefore, the

soil must be able to stand unsupported for a certain period of time, depending on

nail installation progress and the length of the excavated row (length of wall).

This would require the soil to have a sufficient degree of cohesion, cementing, orapparent cohesion from moisture. In addition, the anticipated construction

sequencing with regard to the work zone traffic control should be reviewed to

determine the offset to traffic.

B. Seepage: If the groundwater exists within the cut face, the unreinforced soil may

slump locally upon excavation, or the shotcrete to soil bond may be reduced.

C. Soft Clays: The low frictional resistance of soft clay would require a very high

density, of considerable length, of nails. In addition, soil nails in these soils are

susceptible to creep and permanent wall systems may not be practical.

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8. Table identifying the soil parameters used for the design:

SOIL NAIL WALL DESIGN PARAMETERS

Location Elevation

(feet (meters))

Unit

Weight

(pcf (kN/m))

Friction

Angle

(degrees)

Notes: a. Groundwater is assumed at elevation ______.

b. A surcharge load of _____psf (kPa) is to be assumed at the top

of wall.

c. The Contractors attention is directed to the subsurface

conditions at elevation ______ which indicates (choices: rock,

boulders, loose material, obstructions, perched water).d. Any other pertinent information.

If the soil nailed wall is associated with a structure for which a Foundation Design

Report (FDR) has been prepared, the FDR will provide this information. If,

however, an FDR has not been prepared or the soil nailed wall is not in the

vicinity of a structure, this information is to be provided by the GEB or the RGE

for inclusion on the plans.

9. The location of the preproduction verification test nail is to be shown on the

Plans. The specification requires a minimum of 2 verification tests in each

different soil/rock unit and for each different drilling/grouting method proposed tobe used, at each wall location. Verification test nails will be sacrificial and not

incorporated as production nails. The preproduction verification test nail location

will identify the first nail (sacrificial) to be tested to confirm the assumptions of

the Contractors Consultant.

The facing details for permanent soil nail walls are left to the Designer. All appropriate item

numbers should be identified for the permanent facing components as they are not included under

the Basis of Payment in the soil nail specification. The details should include:

1. Connection of the permanent facing to the construction face of the soil nailed wall

system.

2. Required reinforcement (if necessary).

3. Extension of internal and external drainage systems.

4. All appropriate item numbers and details pertinent to the chosen facing (barriers,

coping, color, finishes, etc.).

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The nail tendons will be inspected for rust just prior to installation. Loose,

powdery rust should be rubbed off, but not sanded. Nail tendons with nicks or pits

are to be rejected.

The nail tendon is encapsulated or specified corrosion protection is applied, ifrequired by the contract documents. Bare spots are unacceptable, as even the

smallest pinholes can result in severe corrosion in aggressive soils.

The nail tendons shall be covered and stored off the ground, out of the way of

construction equipment. Encapsulated or epoxy coated corrosion protected nail tendons

shall be stacked with care to prevent damage to the coating or encapsulation.

The Inspector will confirm the mix design of the soil nail grout and facing shotcrete for

compliance with the specification. When required, take grout cubes and/or shotcrete test

panel and core samples for testing.

The Inspector will verify that the geocomposite drainage materials conform to the

requirements of the specification and appear on the Departments Approved List.

D. Monitoring Nail Installation

1. Excavation:

Prior to the start of the wall construction, the Inspector will check for any

variations between the actual ground elevation along the wall line and

those shown on the Approved Shop Drawings.

The Inspector will monitor the excavation operation, frequently scanning

the walls construction site to ensure the Contractor is maintaining overall

stability and no ground deformations have occurred. The Inspector will

check the wall neat line excavation and verify that the Contractor is not

overexcavating into the next lift.

Typically, tension cracks form in the ground surface located immediately

behind the top of the soil nail wall excavation. These cracks should be

located and the Contactor and designer notified of their presence. TheInspector will monitor the cracks and provide displacement data to the

Contractor and designer. Water should not be allowed to enter tension

cracks.

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2. Drilling:

The Inspector will record all appropriate information for each soil nail

installation on a copy of the Soil Nail Installation and Summary Forms

included in this manual. The Inspector will log the soil and rock cuttings

brought up by the drilling operation.

The Inspector will verify the nail hole location. During drilling, the

Inspector will check that the Contractor is utilizing a drill bit that will

produce the proper hole diameter and verify that the nail declination angle

is the same as shown on the Approved Shop Drawings.

The Inspector will continue monitoring to ensure no ground deformations

have occurred or that there is no interconnection between drillholes.

3. Nail Installation:

The Inspector will inspect uncased holes with a mirror or flashlight forcaving or loose debris. The hole shall be open and clean.

The Inspector will check the bonded and temporary unbonded lengths of

the test nails.

The Inspector will ensure that the nail tendon is handled carefully to

prevent damage. The temperature of the nail tendons must be above 32 F

(0 C) to prevent the grout from freezing on contact.

The Inspector will verify that the nails are inserted to the minimum length

shown on the Approved Drawings. If the Contractor is unable to insert the

nail tendon to the minimum length, this unacceptable condition points to a

caving/sloughing hole and/or insufficient drilled length. Never allow the

nail tendon to be driven or pushed beyond the drilled length, or cut off.

4. Grouting:

The Inspector will verify that the grout is batched in accordance with the

approved mix design. The grouting equipment shall be equipped with a

working pressure gauge. The Inspector will monitor and record the groutpressure used. The Contractor shall clean the grout pressure gauge at least

daily to prevent clogging.

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P= load (maximum applied test load, kips (kN)).

L= original length (temporary unbonded length: length from back of reference plate to the

top of the bond length, inches (millimeters).

A= cross sectional area of steel (square inches (square millimeters))

= Youngs modulus of elasticity (typically 29,000 ksi (200 GPa) for steel)

The measured movement of the soil nail head should exceed 80% of the theoretical

elastic movement. This ensures that load is transferred from the soil nail tendon to the

soil only in the bonded length and that additional load transfer is not occurring in the

temporary unbonded length.

The Inspector will verify that the nail length is sufficient to accommodate all test

equipment (or use a coupler if allowed). The dial gauges shall be in proper working order

and have an appropriate travel length (2 in. (50 mm) recommended minimum). The jack

shall be in proper working order and the jack and pressure gauge shall be calibrated as a

set. The calibration curves for the jack and pressure gauge and the load cell shall be

obtained from the Contractor. The jack or pump shall have a bleed-off valve.

The Inspector will check that the load cell and jack are aligned concentrically with one

another and with the soil nail tendon. The dial gauge shall be aligned with the axis line of

the anchor and independent of the nail and testing apparatus. Do not allow the jack to

drop onto or lay on the anchor.

The Inspector will ensure that the load in the anchor does not drop below the alignment

load (AL) identified in the testing criteria. During a creep test, the load shall be held

constant. The load shall be held within 2% of the intended load by use of a load cell.

The creep movement in the verification test is set such that the total movement is less

than 0.08 in. (2 mm) between the 6 minute and 60 minute readings. During a proof test,

the creep portion may be terminated if less than 0.04 in. (1 mm) of movement has

occurred between the 1 minute and 10 minute readings. This criterion has been set to

ensure that the nail design loads can be safely carried throughout the structures service

life.

The Inspector will continue monitoring the testing equipment to ensure that interference

between the jacking set-up and the nail tendon has not occurred due to misalignment.

The Inspector will record all readings and other pertinent information during testing on a

copy of the Soil Nail Test Data Sheet, Elastic Movement, and Test Nail Creep Movement

included in this manual.

At the completion of testing for all test nails, including sacrificial nails, the Inspector will

verify that the unbonded test length has been properly filled with grout. No voids shall be

left in the ground.

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F. Temporary Shotcrete Construction Facing and Drainage Examination:

The Inspector will check that the geocomposite drainage strips, along with all elements of

the wall drainage network, are installed as shown on the Approved Shop Drawings and

are interconnected, providing continuous drainage paths. Maintenance of drainage

continuity and capacity is critical to the overall stability of the soil nail wall system.

The Inspector will verify that the welded wire fabric has been installed at the locations

and to the dimensions shown on the Approved Shop Drawings.

The Inspector will verify that the reinforcing steel has been installed at the locations and

to the dimensions shown on the Approved Shop Drawings.

The Inspector will verify that the shotcrete is batched in accordance with the approved

mix design.

G. Documentation:

The Inspector will make copies of all appropriate forms for nail tendon installation and

testing. Record and log each nail tendon installation which includes: drilling, subsurface

conditions encountered, nail tendon installation, and grouting. Record and plot test results

for each nail tendon.

All forms and calculations shall be complete, accurate and up to date. Log dates, times,and weather conditions on all records. Keep a photographic record along with the written

documentation.

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REFERENCES

Further information on soil nails may be found in such sources as: US Department of

Transportation, Federal Highway Administration, Publications - Geotechnical Engineering -

FHWA

Publication No. FHWA-IF-03-017: Geotechnical Engineering Circular No. 7 Soil Nail Walls,March 2003 and Publication No. FHWA-SA-93-068: Soil Nailing Field Inspectors Manual, Soil

Nail Walls-Demonstration Project 103, April, 1994.

http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfmhttp://www.fhwa.dot.gov/engineering/geotech/library_listing.cfmhttp://www.fhwa.dot.gov/engineering/geotech/library_listing.cfmhttp://www.fhwa.dot.gov/engineering/geotech/library_listing.cfmhttp://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm

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APPENDICIES

FORMS:

The following forms were reproduced from:

US Department of Transportation, Federal Highway Administration, Publication No. FHWA-

SA-93-068: Soil Nailing Field Inspectors Manual, Soil Nail Walls-Demonstration Project 103,

Appendix A, April, 1994.

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Soil Nail Installation and Summary Forms (US Customary Uni ts)

EB 15-025 A-1 of A-5

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Soil Nail Installation and Summary Forms (US Customary Uni ts)

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Soil Nail Installation and Summary Forms (US Customary Uni ts)

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Soil Nail Installation and Summary Forms (I nternational System of Uni ts)

EB 15-025 B-1 of B-5

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Soil Nail Installation and Summary Forms ( I nternational System of Uni ts)

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Soil Nail Installation and Summary Forms (I nternational System of Uni ts)

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